Neurophysiological Diagnostics
Introduction
Spinal nerve roots and radiculopathy
Upper extremities
Nerve conduction studies. Nerve conduction studying are used to determine if nerve damage is present on motor and sensory neurons. A stimulating and recording electrode are placed over a nerve (e.g. the Ulner or Median nerve). The time it takes for the impulse to reach the recording electrode is termed the latency. Latencies are on the order of milliseconds. The conduction velocity is calculated by dividing the distance between the electrodes by the latency, which equals the conduction velocity.
Lower extremities
The bulbocavernosus reflex or Osinski reflex can be monitored to test for S2-4 nerve root function. The bulbocavernosus reflex is a reflex arc. The dorsal nerve (a branch of the pudendal nerve) carries sensory information from the genitals to the spinal cord via S2-4 nerve roots. Some fibers of the dorsal nerve synapse onto interneurons of the spinal cord that make synaptic connections with motor neurons that innervate the bulbocavernosus muscle, causing the rectum to contract. This pathway can be monitored by placing stimulating electrodes along the sensory nerve of the genitals and recording electrodes on the rectum.